Rendering Prebuilt Images

If you are implementing GDI+, you are probably planning to do one of two things: Render an existing image or draw your own image. You will cover rendering an existing image first, as it is the easier of the two processes.

Here's the process in a nutshell. Load the image. Draw the image. That's it. And it can be done in one line, too!

 g->DrawImageUnscaled(Image::FromFile(S"MCppCover.jpg"), 0.0, 0.0); 

Of course, if you want a little more control, there is another DrawImage() method that you can work with. The Image class has a few members (see Table 11-15) with which you can manipulate the image.

Table 11-15: Common Image Class Members

MEMBER	DESCRIPTION
FromFile()	Static method to load an image from a file
FromHbitmap()	Static method to load a bitmap from a Windows handle
FromStream()	Static method to load an image from a stream
GetBounds()	Returns a bounding rectangle for the image
Height	Specifies the height of the image
HorizontalResolution	Specifies the horizontal resolution of the image in pixels per inch
PhysicalDimensions	Specifies the size of the image
RotateFlip()	Rotates, flips, or rotates and flips the image
Save()	Saves the file to a stream
Size	Specifies the size of the image
VerticalResolution	Specifies the vertical resolution of the image in pixels per inch
Width	Specifies the width of the image

Before you can render an image, you need to load it from some source, either from a file as shown previously or a data stream (maybe the Internet?). Once the image is loaded, the Image class provides you the ability to flip and rotate the image.

Note

The Image class doesn't use the GraphicsUnit, as you might expect. Instead, it uses pixels per inch.

Once you have an image, you're ready to render it. You've seen the Graphics class's DrawImageUnscaled() method. That is about the extent of the functionality it provides. It can take an image and the location where you want to place it. A more flexible rendering method is DrawImage(). It takes myriad overloads (you can examine them at your leisure within the .NET Framework documentation), but the most useful overload takes the image and stretches it to the size you want (see Listing 11-14).

Listing 11-14: Stretching an Image

 namespace DrawImage {     using namespace System;     using namespace System::ComponentModel;     using namespace System::Collections;     using namespace System::Windows::Forms;     using namespace System::Data;     using namespace System::Drawing;     public __gc class Forml : public System::Windows::Forms::Form     {     public:         Form1(void)         //...     protected:         void Dispose(Boolean disposing)         //...     private: System::ComponentModel::Container * components;         void InitializeComponent(void)         {             this->AutoScaleBaseSize = System::Drawing::Size(6, 15);             this->ClientSize = System::Drawing::Size(292, 265);             this->Name = S"Form1";             this->Text = S"Draw Image";             this->Paint +=                 new System::Windows::Forms::PaintEventHandler(this,Form1_Paint);         }     private:         System::Void Form1_Paint(System::Object * sender,                                    System::Windows::Forms::PaintEventArgs * e)         {             Graphics *g = e->Graphics;             Image *img = Image::FromFile(S"MCppCover.jpg");             g->DrawImage(img, 0, 0, img->Width*2, img->Height*2);         }     }; } 

Figure 11-14 shows the end result of DrawImage.exe, which doubles the image with the DrawImage() method. It is a little blurry but not too bad.

Figure 11-14: Doubling an image's size

One last note about rendering images. So far you have only loaded images from files of type .jpg, but you can actually load .bmp, .gif, .png, and .tif image files without having to change a single line of code other than the name of the file.